The objective of this application is to investigate the role of kallistatin in protection against cardiac injury induced by hypertension and ischemic heart disease. Kallistatin was discovered, purified and cloned in our laboratory as a specific tissue kallikrein-binding protein and a unique serine proteinase inhibitor. Purified kallistatin is a potent new vasodilator as it directly induces vasorelaxation and reduces blood pressure independent of its kallikrein inhibitory activity. Transgenic mice overexpressing kallistatin are hypotensive, and kallistatin gene delivery in hypertensive rats causes a prolonged reduction of blood pressure. Furthermore, circulating kallistatin levels are markedly reduced in animal models of hypertension, cardiac and renal dysfunction associated with increased inflammation and oxidative stress. These findings suggest a potential role of kallistatin in inflammation-related hypertension and cardiovascular disease. Our recent studies showed that kallistatin gene transfer reduced inflammatory cytokines and joint swelling in collagen-induced arthritis, and reduced inflammatory cell infiltration and apoptosis in the ischemic heart after ischemia/reperfusion (I/R). Based on these new findings, we hypothesize that kallistatin protects against hypertension and ischemic heart disease by inhibiting oxidative stress, inflammation and cardiomyocyte apoptosis. In order to test this hypothesis, we will pursue the following specific aims: 1) to determine the structural elements of kallistatin required for inhibiting inflammation and cardiomyocyte apoptosis after myocardial I/R, 2) to determine the signaling pathways mediated by kallistatin in inhibiting inflammation after myocardial I/R, 3) to determine the signaling pathways mediated by kallistatin in inhibiting apoptosis after myocardial I/R, and 4) to determine the protective role of endogenous kallistatin in hypertension and ischemic heart disease using kallistatin knockout mice and kallistatin knockdown rats by RNA interference. This research proposal should provide significant insights into the role and regulatory mechanisms of kallistatin in the cardiovascular system, and foster the development of therapeutic agents for halting inflammation-related hypertension and ischemic heart disease.